In order to provide multi-channel voice/data communications over a broad geographical area, wireless- (e.g., cellular-) communication service providers currently install transceiver base stations in protected an maintainable facilities (e.g., buildings). Because of the substantial amount of hardware currently employed to implement the signal processing equipment for a single cellular channel, each base-station is typically configured to provide multichannel communiation capability for only a limited portion of the frequency spectrum that is available to the service provider. A typical base-station may contain three to five racks of equipment, which house multiple sets of discrete receiver and transmitter signal-processing components in order to service a prescribed portion (e.g., 48) of the total number (e.g., 12 MHz) bandwidth.
The receiver section of a typical one of a base station's plurality (e.g., 48) of narrowband (30 kHz) channel units is diagrammatically illustrated in FIG. 1 as comprising a dedicated set of signal processing components, including a front end, down-conversion section 10, an intermediate frequency (IF) section 20, and a baseband section 30. Frontend section 10 comprises a low-noise amplifier 11 to which the transceiver site's antenna is coupled, a radio-frequency-to-intermediate-frequency (RF-IF) down-converting mixer 13, and an associated IF local oscillator 15. IF section 20 comprises a bandpass filter 21 that receives the mixer-13 output, an amplifier 23, an IF-baseband mixer 25, and an associated baseband local oscillator 27. Bandpass filter 21 may have a bandwidth of 100 KHz centered at a respective one of the four hundred 30 KHz sub-portions of a 12-MHz-wide cellular voice/data communication band, diagrammatically illustrated in the multi-channel spectral distribution plot of FIG. 2.
Baseband section 30 contains a lowpass (anti-aliasing) filter 31, an analog-to-digital (A-D) converter 33, a digital (demodulator/error correction) processing unit 35, and an associated telephony (e.g., T1 carrier) unit 37 through which the processed channel signals are coupled to attendant telephony-system equipment. The sampling rate of the A-D converter 33 is typically on the order of 75 kilosamples/sec. The narrowband channel signal as digitized by A-D converter 33 is demodulated by processing unit 35 to recover the embedded voice/data signal for application to telephony carrier unit 37. (A similar dedicated signal processing transmitter section, complementary to the receiver section, is coupled to receive a digital feed from the telephony system equipment and output an up-converted RF signal to the transceiver site's antenna.)
To optimize service coverage within the entire bandwidth (e.g., 10-12 MHz) available to the service provider and to ensure non-interfering coverage among dispersed transceiver sites at which the base stations are located, the transceiver sites in a typical urban service area customarily are geographically distributed in mutually contiguous hex-cells (arranged in a seven-cell set). Each cell has its own limited-capacity multi-rack base station that serves a different respective subset of the available (400) channels. Over a broad geographical area, the frequency allocation within respective cells and the separation between adjacent cell sets may be prescribed to prevent interference among network channels.
Every channel has components spread over multiple equipment racks in a typical channel receiver section of the type described above with reference to FIG. 1, so the cost and labor involved in geographically situating, installing, and maintaining such equipment are substantial. The service provider would therefrom benefit from equipment that is more flexible both in terms of where it can be located and in terms of the particular channels that a given transceiver site can cover. This is particularly true in non-urban areas, where desired cellular coverage may be concentrated along a highway, for which the limited capacity of a conventional 48-channel transceiver site would be inadequate, and where a relatively large, secure, and protective structure for the multiple racks of equipment required may not be readily available.